The invention relates to a connection of a thin metal sheet, forming a substructure, by a screw to a plastics component having a through-bore and having a seal located between the substructure and the component, wherein the connection is produced with a screw having a shank with a thread-cutting or self-tapping thread and with a tip.
A screw of the abovementioned type is known from the document DE 10 2008 045 412 A1. This document also discloses a connection which corresponds essentially to the abovementioned connection. However, in the case of the known connection, a conical sealing disk is arranged between the screw head and the component, and the upper thread section is additionally coated with a sealing means. A sealing profile is located between the component and the substructure.
The known screw connects a profile, which is a threshold, a door frame part or window frame part, to an outer wall in an opening in a building. The upper thread section of the screw is coated with the sealing means. The sealing disk rests in a sealing manner on the profile. The sealing means fills and seals off any space between the support thread and an internal thread of the bore in the profile. The upper thread section serves as a support thread. The thread engagement between the support thread and the profile prevents a relative movement between the profile and the screw. Sealing is achievable between this screw and the profile only because both are precisely coordinated with one another. Such sealing would not be readily achievable if the screw were to be used to fasten photovoltaic elements to trapezoidal sheet metal on a roof. The upper thread section having a larger thread outside diameter would tend to be disruptive in this case. Furthermore, a conical sealing disk would only be usable when the screw has a head, this not necessarily always being the case, and use is usually made, between the trapezoidal sheet metal and the photovoltaic elements, of holding elements, frequently made of plastics material, in the region of which sealing would in any case only be achievable with difficulty. If screws without a head are used, the problem otherwise arises that the lower thread section can be stripped in the trapezoidal sheet metal.
A screw having a shank and a head for fastening a component to a substructure with a conical sealing disk being pressed tightly against the component is already known from the document DE 10 2006 041 860 A1. In this case, the screw head is configured as a cone on its underside about the shank. The cone angle of the conical sealing disk is equal to or greater than the cone angle of the screw head. On account of the conical configuration of the underside of the screw head, what is known as “dishing” of the sealing disk when the screw is tightened is avoided. Such screws are preferably used for mounting steel profile panels for roof, wall and ceiling constructions. The sealing disks usually consist of a metal rear, on which an elastomer layer made of EPDM is vulcanized in an inseparable manner. For thin metal sheet connections, as are intended to be produced in the case of trapezoidal sheet metal, such a screw is less suitable on account of the high force with which it has to be tightened. The risk that the thread will be stripped in the trapezoidal sheet metal would be too high.
The document WO 02/40803 A1 discloses a device and a method for fastening a roof sealing web. Together with the screw, use is made of a holding element, into which an upper thread section is screwed. The screw has a lower thread section having a smaller diameter, which is screwed into a roof substructure. The connection produced in this way is complicated because a specifically designed holding element is required. In order to achieve complete sealing, after the screw has been set, a liquid film is poured into a recess between the holding element and the screw head. Therefore, such a screw connection is likewise less suitable for use in the photovoltaic field.
The document EP 1 015 774 B1 discloses the fastening of wooden battens to a roof or wall substructure consisting inter alia of wood. The screw used in this fastening has on its shank in each case a thread section adjoining the boring tip and the head. These two thread sections have the same outside diameter. In order that wooden battens can be fastened to a roof or wall substructure consisting of wood in a manner resting thereon in a firmly pressed manner, the thread section adjoining the head has a thread pitch which is smaller than the thread pitch of the thread section adjoining the boring tip. The head of the screw is small and formed in a countersinkable manner. Sealing considerations play no part in this connection. There is mutual firm pressing between the batten and the substructure, as a result of which relatively small changes in size, dependent on air humidity, in the region of the batten and likewise in the region of the substructure can be supported.
The document DE 201 21 563 U1 discloses a screw for fastening a formwork panel to a metal formwork girder, having a shank provided with a thread, which is intended to pass through the formwork panel and to come into thread engagement with the formwork girder, wherein the screw is provided with a boring part, an expendable device is provided in the region of the boring part for widening a bore produced in the formwork panel by the boring part, and the shank provided with a thread has a tool engagement end for a screwing-in tool and, next to the tool engagement end, a thread part which has a larger diameter than the remaining thread part. The thread part having a larger diameter has a smaller pitch than the remaining thread part. When a formwork panel is fastened, a connection is produced, in which sealing between the screw and the formwork panel does not matter. This known screw is also only usable when, as in the present case, a substructure provides sufficient resistance in order to shear off the boring wings of which the expendable device consists. Therefore, the known screw would be suitable only to a limited extent to produce a thin metal sheet connection.
The document DE 295 02 068 U1 shows a screw for connecting a window frame, consisting of plastics material, to a cuboidal steel profile. The screw has an upper thread section and a lower thread section, wherein a conically narrowing transition section of the screw shank is arranged between the upper and the lower thread section. The screw is used in a plastics window frame in which a steel profile is used for reinforcement.